JP4519554B2 - Optical disc and manufacturing method thereof - Google Patents

Description

  The present invention relates to a method of manufacturing an optical disc manufactured by transferring irregularities formed on a stamper and an optical disc manufactured using the method.

  In recent years, not only character information but also still image information and moving image information are recorded on a medium. Among them, optical discs that irradiate the disc surface with laser light, detect the reflected light, and read data are widely used from the viewpoint of large capacity and long-term storage.

  A DVD (Digital Versatile Disc), which is a large-capacity optical disk, has been standardized, and a disk with a diameter of 120 mm and a capacity of 4.7 GB on one side is commercially available. In contrast, for example, Non-Patent Document 1 proposes a higher density. In this case, the thickness of the light transmitting cover layer is set to 0.1 mm. And in order to acquire the rigidity as a disk, it has the structure bonded together with a thick board | substrate.

  In order to increase the recording capacity, there are a reduction in the wavelength of the laser beam and an increase in the numerical aperture of the objective lens. When the numerical aperture of the objective lens is increased, the spot of the irradiated laser beam is reduced, and the density can be increased. However, when the numerical aperture of the objective lens is increased, the focal length is shortened and the influence of the tilt of the optical axis and the disc incident surface is greatly increased. Therefore, it is necessary to thin the light transmission layer (cover layer) on the side on which the laser light is incident.

  However, since there is a limit to thinning the substrate by injection molding, it is difficult to increase the recording capacity by this method. In view of this, an optical disc has been developed in which a light transmission layer that transmits laser light is formed on a substrate, and a metal thin film (reflection layer) is irradiated with laser light through the light transmission layer. Currently, there is a standard for single-sided 23 GB to 27 GB for a Blu-ray disc which is a next generation optical disc.

  As another method for producing an optical disk, for example, Patent Document 1 discloses a method in which a thermoplastic resin layer is provided on a resin flat plate, and the thermoplastic resin layer is heated and pressed against a stamper having projections and depressions. Further, Patent Document 2 discloses a method in which any one of an ultraviolet curable resin, an electron beam curable resin, and a thermosetting resin is provided on a thin film and then pressed with a stamper.

FIG. 8 shows an outline of the optical disk manufacturing process according to the method of Patent Document 1. In FIG. 8A, a thermoplastic resin layer 102 is provided on the substrate 101. When the surface of the thermoplastic resin layer 102 is heated and pressure-contacted with the stamper 103 having irregularities formed thereon, the irregularities of the stamper 103 are transferred to the thermoplastic resin layer 102 as shown in FIG. Thereafter, as shown in FIG. 8C, a metal thin film 104 or the like as a reflective layer is formed on the thermoplastic resin layer 102 by, for example, a vacuum film forming apparatus. Finally, as shown in FIG. 8D, a cover layer 105 is provided on the metal thin film 104 to form an optical disk.
Yamamoto, “High-capacity optical disk with 12Gbyte on one side”, O plus E, 20 (No.2), p.183-186 (1998). JP-A-8-124224 Japanese Patent Laid-Open No. 1-138636

  In order to increase the recording density of the optical disc, it is necessary to make the cover layer 105 thin as described above. And in order to acquire rigidity, the structure bonded together with the thick board | substrate 101 is requested | required.

  In the method disclosed in Patent Document 1, a thermoplastic resin layer 102 provided on a substrate 101 is heated and pressed against a stamper 103 having projections and depressions, and then a metal thin film 104 is provided. As described above, when the metal thin film 104 is provided after the unevenness is formed on the thermoplastic resin layer 102, the shape of the unevenness on the upper surface and the lower surface of the reflective layer 104 is different as shown in FIG. That is, the lower surface of the metal thin film 104 well reflects the shape of the unevenness formed on the thermoplastic resin layer 102, whereas the unevenness on the upper surface of the metal thin film 104 is duller than the other. Shape. Therefore, when the laser light is incident on the metal thin film 104 from above in FIG. 8D, unnecessary irregular reflection occurs due to the dullness of the uneven corner. This effect can be ignored when the recording density is low. However, as the recording density increases, this irregular reflection adversely affects the signal, and reading errors tend to occur.

  As a method of coping with this, for example, it is conceivable to form the metal thin film 104 on the surface on which the irregularities are formed after the irregularities are formed on the cover layer 105 on which the laser light is incident. However, it is almost impossible to produce a cover layer 105 having a thickness of 0.1 mm in which irregularities are formed by injection molding as used in producing the substrate 101. Therefore, based on the technique of Patent Document 1, it is conceivable that a thermoplastic resin is provided on a thin sheet so as to have a thickness of about 0.1 mm in total, and is heated and pressed against the stamper. However, if the thickness is reduced in this way, the rigidity is low, and the degree of thermal contraction varies from place to place due to temperature unevenness during heating. As a result, there arises a problem that wrinkles are generated on the whole. Similarly, wrinkles due to shrinkage are also generated by the method of Patent Document 2 in which a layer made of any one of an ultraviolet curable resin, an electron beam curable resin, and a thermosetting resin is provided on a sheet and pressed against a stamper. Furthermore, there is a problem that the adhesion between the sheet and the resin is weak.

  The present invention has been made in view of such a situation, the signal is not affected by the thickness of the metal thin film, and the method of manufacturing an optical disc excellent in productivity without wrinkles or delamination, and An object of the present invention is to provide an optical disk manufactured using the optical disk.

  The invention according to claim 1 is a method of manufacturing an optical disc in which laser light is irradiated from the opposite side to the substrate when reading information, and after the thin film including at least a metal reflection layer is formed on the substrate, the thin film In this optical disk manufacturing method, a stamper having unevenness on the side is directly pressed against the thin film, and the unevenness is transferred to the metal reflective layer.

  According to a second aspect of the present invention, in the optical disk manufacturing method according to the first aspect, the thin film is a flat substrate made of a thermoplastic resin formed on or on a substrate having a flat surface made of a thermoplastic resin. It is formed on a resin layer having a surface.

  According to a third aspect of the present invention, in the optical disk manufacturing method according to the first or second aspect, the stamper is heated to a temperature equal to or higher than a softening temperature of the thermoplastic resin.

  According to a fourth aspect of the present invention, in the optical disc manufacturing method according to any one of the first to third aspects, the thin film has a thickness that is approximately three times or more the height of the convex portion of the stamper. It is formed on a substrate.

  According to a fifth aspect of the present invention, in the method of manufacturing an optical disk according to any one of the first to fourth aspects, the multilayer film including the metal reflective layer and another layer is used as the thin film, and the metal reflective layer is the stamper. It is formed so that it may be located on the opposite side.

  According to a sixth aspect of the present invention, in the method for manufacturing an optical disc according to any one of the first to fifth aspects, the thin film is vacuum-sucked toward the stamper when the thin film and the stamper are pressed against each other. Features.

  According to a seventh aspect of the present invention, in the optical disc manufacturing method according to any one of the first to sixth aspects, a thermoplastic resin layer is formed on the thin film, and at least a metal reflective layer is included on the thermoplastic resin layer. After the thin film is formed, a stamper having unevenness on the thin film side is directly pressed against the thin film, and the unevenness is transferred to the metal reflective layer.

  According to an eighth aspect of the present invention, in the optical disk manufacturing method according to any one of the first to seventh aspects, a light transmission layer made of a transparent sheet or an ultraviolet curable resin is provided on the thin film.

  The invention according to claim 9 is a method of manufacturing an optical disc in which laser light is irradiated from the side opposite to the substrate when reading information, and includes at least a metal reflection layer on the surface of a stamper fixed in a mold and having unevenness. In this optical disk manufacturing method, the substrate is formed by injecting molten resin into the mold after the metal reflecting layer side of the sheet member is directly adhered.

  According to a tenth aspect of the present invention, in the optical disk manufacturing method according to the ninth aspect, at least the vicinity of the center of the sheet member is vacuum-sucked to the stamper side during the injection of the molten resin.

  The invention according to claim 11 is the method of manufacturing an optical disc according to claim 9 or 10, wherein the sheet member includes a resin sheet in which at least a metal reflective layer is formed on a resin layer, and the resin layer is continuous over the entire surface. In this case, a hole is formed in the central portion of the resin layer after filling with the molten resin.

  According to a twelfth aspect of the present invention, in the optical disk manufacturing method according to the eleventh aspect, the metal reflective layer is provided in addition to the central portion of the resin sheet.

  According to a thirteenth aspect of the present invention, in the optical disk manufacturing method according to the eleventh or twelfth aspect, a substrate is formed by injecting molten resin made of the same kind of resin as the resin layer of the resin sheet into the mold. It is characterized by being.

  According to a fourteenth aspect of the present invention, in the optical disc manufacturing method according to any one of the ninth to thirteenth aspects, the outer diameter of the sheet member is smaller than the inner diameter of the cavity of the mold.

  According to a fifteenth aspect of the present invention, in the optical disk manufacturing method according to any of the ninth to fourteenth aspects, the stamper is disposed on a surface opposite to a surface having a hole through which the molten resin of the mold is injected. It is characterized by that.

  According to a sixteenth aspect of the present invention, in the optical disk manufacturing method according to any one of the first to fifteenth aspects, the metal reflective layer includes at least one of Au, Ag, Cu, Pt, and Al at 95 wt% or more. A metal film is formed.

  According to a seventeenth aspect of the present invention, in the optical disk manufacturing method according to any one of the ninth to sixteenth aspects, the metal reflective layer and other layers are arranged so that the metal reflective layer is located on the side opposite to the stamper. A thin film is formed.

  The invention according to claim 18 is the method of manufacturing an optical disc according to any one of claims 9 to 17, wherein a thermoplastic resin layer is formed on the sheet member, and at least a metal reflective layer is formed on the thermoplastic resin layer. After the thin film is formed, the stamper having unevenness on the thin film side is directly heated and pressed against the thin film, and the unevenness is transferred to the metal reflective layer.

  According to a nineteenth aspect of the present invention, in the optical disk manufacturing method according to any one of the ninth to eighteenth aspects, a light transmissive layer made of a transparent sheet or an ultraviolet curable resin is provided on the sheet member.

  In the invention described in claim 20, the radius of curvature of the uneven edge portion formed on the surface irradiated with the laser beam in the thin film is smaller than the radius of curvature of the uneven edge portion formed on the opposite surface of the thin film. It is an optical disk.

  According to the method for manufacturing an optical disk of the present invention, the stamper is directly pressed against the thin film, so that the unevenness of the stamper is accurately transferred to the metal reflection layer. Therefore, accurate signal reading becomes possible. Furthermore, since the optimum uneven shape can be determined by the uneven shape of the stamper, the signal can be easily optimized.

  According to another method of manufacturing an optical disc of the present invention, the surface having the unevenness of the stamper and the metal reflection layer side of the sheet member including at least the metal reflection layer are in direct contact with each other. And molten resin is inject | emitted in the cavity on the opposite side to the metal reflective layer side, and a board | substrate is formed. At this time, the stamper, the metal reflection layer, and the substrate are pressed against each other by the mold. As a result, the unevenness of the stamper is accurately transferred to the metal reflective layer that is in pressure contact with the surface having the unevenness of the stamper.

  According to the optical disk of the present invention, in the thin film, when the uneven edge formed on the surface irradiated with the laser beam is compared with the uneven edge formed on the opposite surface, the former radius of curvature is obtained. Is small, that is, it has good squareness. Therefore, accurate signal reading becomes possible.

  Embodiments of an optical disk manufacturing method according to the present invention will be described below with reference to the drawings. The shape and size of the optical disk are appropriately determined depending on the application of the optical disk. For example, in the case of a DVD, the disk has a disk shape with a diameter of 120 mm and a central hole with a diameter of 15 mm at the center. The thickness is usually about 1.2 mm.

[First Embodiment]
FIG. 1 is a schematic process diagram for explaining a method of manufacturing an optical disc according to the first embodiment of the present invention.

  First, in the step shown in FIG. 1A, a 50 μm thick acrylic resin (softening temperature to 90 ° C.) film is formed on a 1.1 mm thick substrate 1 made of polycarbonate resin (softening temperature to 140 ° C.). The thermoplastic resin layer 2 is bonded together with an adhesive. Then, a silver (Ag) thin film 3 is formed on the thermoplastic resin layer 2 to a thickness of 50 nm by sputtering. Further, as the unevenness of the stamper 4 corresponding to the information signal, one having a convex pit having a track pitch of 0.35 μm and a height of 70 nm (the height of the convex portion is 70 nm) was used. The stamper 4 is attached to a press apparatus, and the substrate 1 provided with the thermoplastic resin layer 2 and the thin film 3 is attached to the side facing it. The stamper 4 is heated to a temperature necessary for plastic deformation of the thermoplastic resin layer 2. In the above configuration, the softening temperature of the substrate 1 is about 140 ° C., and that of the thermoplastic resin layer 2 is about 90 ° C. For this reason, it is desirable that the temperature of the stamper 4 is set to a temperature at which the thermoplastic resin layer 2 is deformed but the substrate 1 is not deformed, that is, between 100-130 ° C. In the present embodiment, the temperature of the stamper 4 is set to 120 ° C.

  Here, since the substrate 1 is elastically deformed at this temperature, it returns to its original state even if it is deformed once. On the other hand, at this temperature, the thermoplastic resin layer 2 is plastically deformed. In this state, the stamper 4 is brought into pressure contact with the thin film 3 at a surface pressure of 50 MPa. At this time, it is desirable to suck the gap between the thin film 3 and the stamper 4 in a vacuum so that bubbles do not enter. This prevents gas entrainment and enables effective pressure welding. As a result, the unevenness of the stamper 4 is accurately transferred to the thin film 3 as in the step shown in FIG. At this time, not only the thin film 3 but also the thermoplastic resin layer 2 is plastically deformed simultaneously.

  Subsequently, as in the step shown in FIG. 1C, the cover layer 5 is formed on the thin film 3 to complete the optical disc. The cover layer 5 serves to protect the irregularities formed on the thin film 3. Further, since the unevenness is read through the cover layer 5, it is necessary not to prevent the transmission of the laser light. Here, as the cover layer 5, an ultraviolet curable resin was applied, and the cover layer 5 was cured by being irradiated with ultraviolet rays after spin coating. The thickness of the cover layer 5 obtained as a result is about 0.1 mm. The cover layer 5 may be configured to adhere a transparent sheet made of polycarbonate resin or the like.

  The thermoplastic resin layer 2 is a resin that causes plastic deformation when a predetermined force is applied at the softening temperature or higher, and is selected from a resin group including an acrylic resin, a polycarbonate resin, a polyolefin resin, and the like. Moreover, the thickness of the thermoplastic resin layer 2 is 20 micrometers-100 micrometers, More preferably, it is 50 micrometers.

  Further, when the substrate 1 and the thermoplastic resin layer 2 are combined, it is desirable that the softening temperature of the thermoplastic resin layer 2 is lower than the softening temperature of the substrate 1. This is because, when the stamper 4 and the thermoplastic resin layer 2 are heated and pressed, the substrate 1 is not plastically deformed, and the flatness of the substrate 1 can be maintained by plastically deforming the thermoplastic resin layer 2. is there.

  The thin film 3 is only a metal reflection layer in the case of a reproduction type (DVD-ROM), but is a multilayer film including a recording layer and a metal reflection layer in the case of a write-once type or a rewritable type (DVD-RAM). is there. In the case of the regenerative type described in the present embodiment, the unevenness of the stamper 4 is directly transferred to the thin film 3, so that a metal having high ductility is desirable. For example, in addition to silver used in this embodiment, gold (Au), copper (Cu), platinum (Pt), and aluminum (Al) are exemplified as elements having such characteristics. Furthermore, not only the above simple substance but also an alloy containing these may be used. In the present invention, the thin film 3 may be a material containing 95 wt% or more, preferably 97 wt% or more, more preferably 98 wt% or more of gold, silver, copper, platinum, and aluminum. This is because when 5 wt% or more of other materials are added, the ductility is greatly reduced or the rigidity is greatly increased. The above-described conditions required for the thin film are the same in other embodiments according to the present invention.

  The stamper 4 has unevenness corresponding to an information signal, and bears a role of transferring the unevenness to the thin film 3 by being pressed. The stamper 4 is made of, for example, nickel (Ni), and the unevenness is formed by a normal photoresist method or the like.

  As a method for forming the thermoplastic resin layer 2 on the substrate 1, as used in this embodiment, there is a method in which a sheet of thermoplastic resin is placed on the substrate 1 and bonded with an adhesive. In addition, for example, there is a method in which a sheet of a thermoplastic resin is placed on the substrate 1 and manufactured by coextrusion lamination. Any of these is a desirable method because bubbles are hardly involved between the substrate 1 and the thermoplastic resin layer 2 or poor adhesion occurs. Further, as a method of forming the thin film 3 on the thermoplastic resin layer 2, a vacuum film forming method other than the sputtering method may be used.

  Subsequently, under the same conditions as described above, only the wall surface angle of the unevenness of the stamper 4 was changed, and the transfer characteristics were examined. Here, as shown in FIG. 2, the uneven wall surface angle is an angle θ (range from 0 to 90 degrees) to the wall surface of the convex portion on the basis of the plane when there is no convex portion of the stamper 4 as shown in FIG. ). That is, θ = 0 degrees in the plane, and θ = 90 degrees in the case of having a wall surface perpendicular to the plane. As a result, the uneven shape of the stamper 4 was accurately transferred to the thin film 3 when the wall surface angle θ of the unevenness was 70 degrees or less. In other words, when the uneven wall surface angle θ of the stamper 4 was 70 degrees or less, the uneven wall surface angle θ of the stamper 4 and the uneven wall surface angle transferred to the thin film 3 showed good agreement. That is, when the wall surface angle θ of the unevenness of the stamper 4 exceeds 70 degrees and is 80 degrees or 90 degrees, the transfer to the thin film 3 is insufficient. On the other hand, when the wall surface angle θ of the unevenness of the stamper 4 is small, 70 degrees or less, 50 degrees or 60 degrees, the transfer is performed effectively, and the wall surface angle of the unevenness of the stamper 4 and the thin film 3 is in good agreement. Indicated.

  Furthermore, the cross-section observation of the produced optical disk was performed using the transmission electron microscope (Transmission Electron Microscope; TEM). As a result, first, the film thickness of the uneven wall surface of the thin film 3 was substantially the same in both the radial direction and the circumferential direction. In other words, the pressure at the time of pressure contact is approximately isotropic.

Further, in the thin film 3, the edge of the concave portion of the surface (upper surface in FIG. 1) in close contact with the stamper 4 and the edge of the convex portion of the surface in close contact with the thermoplastic resin layer 2 (lower surface in FIG. 1). Examined. As a result, it was found that the radius of curvature of the edge brought into close contact with the stamper 4 was smaller and a good edge was formed. Here, as shown in FIG. 1 (b), if the radius of curvature of the edge in close contact with the stamper 4 is R ₁ and the radius of curvature of the edge in close contact with the thermoplastic resin layer 2 is R ₂ , R ₂ / R ₁ > 1.0, preferably R ₂ / R ₁ > 1.5, more preferably R ₂ / R ₁ > 2.0.

However, the edge is rarely a smooth curved surface, and is often a surface having irregularities. In order to explain this, FIG. 3 shows a schematic cross-sectional view enlarging a part of FIG. When the edge does not change smoothly as described above, as indicated by a dotted line in FIG. 3, the edge may be approximated by an arc and a circle having this arc may be considered. For example, let P _{1 be} the point where the surface with the irregularities of the edge is away from the line extending the bottom surface of the recess on the upper surface of the thin film 3, and Q ₁ is the point where it is away from the line extending the wall surface of the recess on the upper surface of the thin film 3. Then, using these two points as fixed points, an approximate arc is obtained such that the difference from the unevenness of the edge becomes smaller than a predetermined value by the least square method or the like. The radius of the circle having this arc as a part of the circle is the curvature radius R ₁ . Similarly, let P _{2 be} the point where the surface having the irregularities of the edge is separated from the undeformed lower surface of the thin film 3, and Q ₂ be the point away from the line extending from the wall surface of the projection on the lower surface of the thin film 3. Radius of approximate circle obtained the two points as a fixed point, a radius of curvature R _2.

  As described above, the shape of the irregularities formed on the thin film 3 reproduces the shape of the stamper 4 well. Therefore, unnecessary irregular reflection does not occur with respect to the laser light incident from the cover layer 5 side, and the signal is read accurately. Generally, the thicker the thin film 3, the more difficult the upper surface of the thin film 3 reflects the irregularities of the base. On the other hand, according to the present invention, since the unevenness is transferred after the thin film 3 is formed, there is no influence such as a dull edge of the unevenness due to the thickness of the thin film 3. Therefore, the optimum uneven shape can be determined by the uneven shape of the stamper 4, and signal optimization is easy.

  In the present embodiment, the substrate 1 provided with the thermoplastic resin layer 2 is a polycarbonate resin and has a high rigidity because the thickness is 1.1 mm. Further, the heated stamper 4 and the thermoplastic resin layer 2 are not directly pressed, but are pressed through a thin film 3 having a higher thermal conductivity than the thermoplastic resin layer 2. Due to the high rigidity of the substrate 1 and the uniform temperature in the surface direction of the thin film 3, the occurrence of wrinkles in the thermoplastic resin layer 2 is suppressed.

  In the present embodiment, the thermoplastic resin layer 2 is further formed on the substrate 1. However, the substrate 1 itself may be made of a thermoplastic resin and the thermoplastic resin layer 2 may be omitted. In general, since the thermoplastic resin has low thermal conductivity, even if the stamper 4 is made higher than the softening temperature of the substrate 1 (thermoplastic resin) and pressed against the thin film 3, the stamper 4 side of the substrate 1 (thermoplastic resin) Only the surface layer rises above the softening temperature. Therefore, even if the thermoplastic resin layer 2 is omitted, the flatness of the entire substrate 1 is not lost.

  In the present embodiment, an acrylic resin (softening temperature to 90 ° C.) is used as the thermoplastic resin layer 2 in order to keep the heating temperature of the stamper 4 low. However, the present invention is not limited to this, and a polycarbonate resin (softening temperature to 140 ° C.) or a polyolefin resin (softening temperature to 120 ° C.) may be used. However, it is desirable that the substrate 1 is not thermally deformed at the softening temperature of the resin used as the thermoplastic resin layer 2. If it is such a material, the board | substrate 1 may be resin other than the polycarbonate resin used by this embodiment, glass, or a metal.

  Further, in the present embodiment, the heating temperature of the stamper 4 is set to be not less than the softening temperature of the thermoplastic resin layer 2 and not more than the softening temperature of the substrate 1. However, the present invention is not limited to this, and the heating temperature of the stamper 4 may be lower than the softening temperature of the thermoplastic resin layer 2. It is mainly temperature and pressure that control the plastic deformation of the thermoplastic resin layer 2. Therefore, even when the temperature is slightly lower than the softening temperature, the unevenness of the stamper 4 can be effectively transferred by increasing the pressure accordingly.

  In the present embodiment, the case where only the metal reflection layer is used as the thin film 3 has been described. However, the present invention is not limited to this, and the thin film 3 may be a multilayer film including a recording film layer and a metal reflection layer. . In this case, the metal reflection layer is not directly pressed against the stamper 4, but the distance between the metal reflection layer having high thermal conductivity and the stamper 4 is very close, so that heat is transmitted at high speed in the surface direction of the metal reflection layer. Therefore, the temperature in the surface direction of the thin film 3 is uniform, and there is also an effect of high rigidity of the substrate 1, so that wrinkles of the thermoplastic resin layer 2 are suppressed.

[Second Embodiment]
In the first embodiment described above, not only the thin film 3 but also the thermoplastic resin layer 2 is plastically deformed by pressing the stamper 4 heated to the softening temperature of the thermoplastic resin layer 2 or higher, so that the stamper 4 Was transferred to the thin film 3. In the present embodiment, an example will be described in which the thermoplastic resin layer 2 is omitted and the thin film 3 on the substrate 1 is directly plastically deformed.

  FIG. 4 is a schematic process diagram for explaining a method of manufacturing an optical disc according to the second embodiment of the present invention.

  First, in the process shown in FIG. 4A, a silver thin film 3 is formed with a thickness of 200 nm on a substrate 1 made of polycarbonate resin and having a thickness of 1.1 mm by a sputtering method. In addition, as the unevenness of the stamper 4 corresponding to the information signal, one having convex pits having a track pitch of 0.35 μm and a height of 70 nm was used. The stamper 4 is attached to a press apparatus, and the substrate 1 provided with the thin film 3 is attached to the side facing the stamper 4. In the first embodiment described above, the stamper 4 is heated to a temperature equal to or higher than the softening temperature of the thermoplastic resin layer 2, but this is not necessary in the present embodiment.

  Here, the experiment was conducted while maintaining the substrate 1 on which the stamper 4 and the thin film 3 were formed at 25 ° C. In this state, the stamper 4 is brought into pressure contact with the thin film 3 at a surface pressure of 100 MPa. At this time, it is desirable to suck the gap between the thin film 3 and the stamper 4 in a vacuum so that bubbles do not enter. Thereby, entrainment of gas can be prevented and pressure welding can be performed effectively. As a result, the unevenness of the stamper 4 is accurately transferred to the thin film 3 as in the step shown in FIG. Subsequently, as shown in FIG. 4C, the cover layer 5 is formed on the thin film 3 to complete the optical disc. Here, the cover layer 5 includes a transparent sheet 6 made of a polycarbonate resin and an adhesive layer 7. The transparent sheet 6 is adhered to the thin film 3 by the adhesive layer 7. The adhesive layer 7 may be an ultraviolet curable resin or an adhesive resin. The thickness of the cover layer 5 obtained as a result is about 0.1 mm.

  The conditions required for the substrate 1 and the thin film 3 are the same as those described in the first embodiment. The thin film 3 is not limited to silver and may be any material having high ductility. The conditions required for the thin film 3 are the same as those shown in the first embodiment.

  In the present embodiment, since the thermoplastic resin layer 2 is omitted, the stamper 4 does not need to be heated to the softening temperature or higher, and may be set to a predetermined temperature in order to keep the transfer characteristics constant. .

  Subsequently, the transfer characteristics when the thickness of the silver thin film 3 was reduced in the same configuration as described above were examined. Specifically, the thickness of the thin film 3 was set to 50 nm, 100 nm, and 150 nm, and the same stamper 4 as described above was used to press the thin film 3 with a surface pressure of 100 MPa. As a result, in any case, the unevenness of the stamper 4 was accurately transferred to the thin film 3. Further, under the same conditions as described above, only the wall surface angle of the unevenness of the stamper 4 was changed, and the transfer characteristics were examined. As a result, when the wall surface angle of the unevenness of the stamper 4 was 70 degrees or less, the angle and the wall surface angle of the unevenness transferred to the thin film 3 showed a good agreement, that is, transferred accurately.

Furthermore, using a transmission electron microscope (TEM), a cross-sectional observation of the optical disk produced with the thin film 3 having a thickness of 50 nm was performed. In this case, although not explicitly shown in FIG. 4, the upper surface of the substrate 1 (and the lower surface of the thin film 3) is also slightly plastically deformed. As a result of observation, first, the film thickness of the uneven wall surface of the thin film 3 was substantially the same in both the radial direction and the circumferential direction. That is, the pressure at the time of the pressure contact is substantially isotropic. Further, it was found that the edge radius of contact with the stamper 4 was smaller and a good edge was formed. Here, as shown in FIG. 1 (b), if the radius of curvature of the edge in close contact with the stamper 4 is R ₁ and the radius of curvature of the edge in close contact with the thermoplastic resin layer 2 is R ₂ , R ₂ / R ₁ > 1.0, preferably R ₂ / R ₁ > 1.5, more preferably R ₂ / R ₁ > 2.0. Further, when the thickness of the thin film 3 becomes 100 nm or more, the plastic deformation of the substrate 1 gradually decreases.

  Subsequently, in the same configuration as described above, the transfer characteristics when the substrate 1 was changed to glass were examined. Specifically, the thickness of the silver thin film 3 was 100 nm, 150 nm, and 200 nm, and the thin film 3 was pressed into contact with the thin film 3 at a surface pressure of 100 MPa using the same stamper 4 as described above. As a result, the transfer of pits was insufficient when the thickness of the thin film 3 was 100 nm and 150 nm, and sufficient transfer was obtained only when the thickness was 200 nm. This is because the substrate 1 is made of glass and has high rigidity and hardly deforms. In other words, since plastic deformation occurs only in the thin film 3, the deformation of the thin film 3 is suppressed with respect to the height of the convex portion of the stamper 4 of 70 nm. Therefore, when the rigidity of the substrate 1 is high, the thickness of the thin film 3 needs to be approximately three times or more the height of the convex portion of the stamper 4.

  As mentioned above, although the case where the board | substrate 1 was a thermoplastic resin and glass was shown, the board | substrate 1 may be other resin or a metal. When the substrate 1 is a metal, if the thickness of the silver thin film 3 is 200 nm or more, the unevenness of the stamper 4 is accurately transferred.

  Next, the transfer characteristics when a multilayer film including a recording layer and a metal reflective layer was used as the thin film 3 were examined. The thin film 3 is composed of, in order from the substrate 1 side, a reflective layer 100 nm made of silver, a transparent film 100 nm made of silicon oxide and zinc sulfide, a recording layer 20 nm made of germanium, tellurium and antimony, and a transparent film 50 nm made of silicon oxide and zinc sulfide. As the unevenness of the stamper 4, the one having convex pits with a track pitch of 0.35 μm and a height of 70 nm was used as described above. Further, the substrate 1 on which the stamper 4 and the thin film 3 were formed was kept at 25 ° C. In this state, the stamper 4 was brought into pressure contact with the thin film 3 at a surface pressure of 150 MPa. As a result, when the wall surface angle of the unevenness of the stamper 4 was 60 degrees or less, the angle and the wall surface angle of the unevenness transferred to the thin film 3 showed good agreement, that is, the stamper 4 was accurately transferred.

  As described above, the shape of the irregularities formed on the thin film 3 reproduces the shape of the stamper 4 well. Therefore, unnecessary irregular reflection does not occur with respect to the laser light incident from the cover layer 5 side, and the signal is read accurately. Generally, the thicker the thin film 3, the more difficult the upper surface of the thin film 3 reflects the irregularities of the base. On the other hand, according to the present invention, since the unevenness is transferred after the thin film 3 is formed, there is no influence such as a dull edge of the unevenness due to the thickness of the thin film 3. Therefore, the optimum uneven shape can be determined by the uneven shape of the stamper 4, and signal optimization is easy.

  Further, in the present embodiment, the transfer is performed by forming the thin film 3 directly on the substrate 1 and pressing the stamper 4 having the unevenness. However, the present invention is not limited to this, and other layers that do not cause thermal deformation may be inserted between the substrate 1 and the thin film 3.

[Third Embodiment]
In the first and second embodiments described above, the unevenness corresponding to the information signal is transferred by pressing the stamper against a thin film or the like sequentially laminated on the substrate. In this embodiment, an example will be described in which a substrate is produced by injection molding and at the same time unevenness is transferred to a thin film.

  FIG. 5 is a schematic cross-sectional view of a mold used in the method of manufacturing an optical disc according to the third embodiment of the present invention. Here, the mold is cylindrical, and FIG. 5 is a cross-sectional view through the central axis. In FIG. 5, the entire mold is composed of a fixed mold 8 and a movable mold 9. The fixed mold 8 is fixed to a molding machine (not shown) by a predetermined method. FIG. 5 shows a state in which the fixed mold 8 and the movable mold 9 are fitted via the spring 20.

  First, the fixed mold 8 includes a fixed side base 10 and a fixed side mirror plate 11 facing the fixed side base 10. This fixed base 10 is a part that is screwed or the like when fixed to a molding machine (not shown). Moreover, the surface on the opposite side of the surface facing the fixed side base | substrate 10 of the fixed side mirror surface board 11 is formed in the mirror surface shape. This is to facilitate the flow of the molten resin. However, when light is not incident from the substrate side, it is not always necessary to use a mirror surface.

  A sprue bush 12 having a hole through which molten resin is injected is formed in the center of the fixed side base 10 and the fixed side specular disk 11. Through this sprue bush 12, molten resin is injected into the mold. Further, an outer peripheral ring 13 for defining an outer diameter of a molded substrate obtained by molding a molten resin is provided outside the fixed side mirror surface plate 11 and is pressed from the fixed mold 8 to the movable mold 9 by a spring 20. ing. Further, the fixed mold 8 has a structure in which air is blown out from the gap between the sprue bush 12 and the fixed-side mirror surface plate 11 (in FIG. 5, an arrow is shown toward a hollow portion in the mold, that is, the cavity. )

  Next, the movable mold 9 has a movable base 19 and a movable mirror plate 17 facing it. This movable base 19 is a part that is screwed or the like when fixed to a molding machine (not shown). Moreover, the surface on the opposite side of the surface facing the movable base 19 of the movable mirror surface board 17 is formed in a mirror shape. A cut punch 14, an ejector 15, and a stamper holder 16 are formed in the center of the movable base 19 and the movable mirror 17 in order from the center axis to the outside. The outer periphery of the stamper holder 16 is in contact with the movable side mirror plate 17. Further, a stamper 18 having unevenness corresponding to an information signal is closely attached to the mirror surface (inside of the mold) of the movable side mirror 17 so that the uneven part is directed toward the inner space (cavity) side of the mold. Yes. The cut punch 14 is for projecting after resin filling to form a hole in the disc, and the ejector 15 is for projecting after resin filling to cause the mold and the disc to peel off. The stamper holder 16 serves to fix the inner periphery of the stamper 18 to the movable side mirror plate 17. The outer periphery of the stamper 18 is fixed by the outer peripheral ring 13 with a clearance for gas escape.

  Further, the movable mold 9 has a structure in which air is blown out or sucked from the gap between the ejector 15 and the stamper holder 16 (in FIG. 5, arrows are directed toward the cavity and from the cavity toward the outside of the mold. showed that). Further, the fixed side base 10 and the movable side specular panel 17 are provided with temperature control water channels (not shown), and are maintained at a constant temperature.

  Further, a circular sheet 31 smaller than the inner diameter of the cavity (the length between the upper and lower outer peripheral rings 13 in FIG. 5) is brought into intimate contact with the surface of the stamper 18 (inside the mold), so that the ejector 15 and the stamper holder 16 Vacuum is sucked from the gap (in FIG. 5, the direction of the arrow from the cavity toward the outside of the mold). Here, the reason why the outer diameter of the sheet 31 is made smaller than the inner diameter of the cavity is that gas escape is sufficient when the molten resin is filled into the mold, so that appearance defects do not occur.

  Here, the sheet 31 has at least a resin layer 32 and a thin film 33. The thin film 33 of the sheet 31 is only a metal reflection layer in the case of the reproduction type, but is a multilayer film having a configuration satisfying signal characteristics including the recording layer and the metal reflection layer in the case of the write-once type and the rewritable type.

  FIGS. 6A and 6B are a plan view (FIG. 6A) and a side view (FIG. 6B) of a resin sheet used in the method of manufacturing an optical disc according to the third embodiment of the present invention. As shown in this figure, the resin layer 32 has no hole in the center, but the thin film 33 has a hole. This is because the thin film 33 is not formed in the central portion, thereby improving the adhesion between the resin layer 32 and a cover layer described later in the central portion.

  Hereinafter, in the present embodiment, it is assumed that the thin film 33 side of the sheet 31 is brought into close contact with the stamper 18 and fixed in the mold. As the unevenness on the stamper 18, one having a convex pit having a track pitch of 0.35 μm and a height of 70 nm was used. Further, the thickness of the sheet 31 is 10 μm, the resin layer 32 is made of polycarbonate resin, and 50 nm of aluminum is formed on the surface as the thin film 33.

  Under such a configuration, molten resin made of polycarbonate resin is injected into the mold through the sprue bush 12. The conditions are a resin temperature of 380 ° C., a mold temperature of 130 ° C., a screw diameter of 25 mm, a maximum injection speed of 200 mm / s, and a tact time of 10 seconds. The stamper 4 reaches the maximum temperature when 0.1 to 0.2 seconds have elapsed after filling the mold. Therefore, at that moment, it is desirable that the pressure with which the filled resin and the sheet 31 are pressed is maximized. As a result, the unevenness of the stamper 18 was accurately transferred to the thin film 33 when the pressure at which the stamper 18 and the sheet 31 were pressed was 150 MPa or more.

  Although there is no hole in the center of the sheet 31, it is formed simultaneously with the resin portion by projecting the cut punch 14 after filling the resin. The obtained disk (molded product) has an inner diameter of 15 mm, an outer diameter of 120 mm, and a thickness of 1.1 mm. The reason why there is no hole in the center of the sheet 31 is to prevent the molten resin from entering between the sheet 31 and the stamper 18 when the resin is filled.

  Further, the stamper 18 is desirably positioned on the movable mold 9 side as shown in FIG. This is because, firstly, the molten resin is injected from the sprue bush 12 on the fixed mold 8 side, so that the sheet 31 is pressed against the stamper 18. The second reason is that the substrate can be removed after being peeled from the stamper 18 stably after the mold is opened.

  And the vacuum suction of the sheet | seat 31 is until immediately after filling of molten resin, and it switches to air blowing at the time of taking out a shaping | molding board | substrate after that. Specific switching may be performed by guiding the vacuum suction circuit and the air blow circuit to the solenoid valve.

  Further, as in the present embodiment, it is desirable that the injected molten resin and the material of the resin layer 32 of the sheet 31 are the same type. In that case, any resin such as acrylic resin, polycarbonate resin, or polyolefin resin may be used. This is because phase separation or the like does not occur if the same type of resin is used, and a good interface is formed. Thereby, the pressure distribution on the resin sheet side of the thin film becomes substantially uniform, and the press contact can be performed effectively. As a result, the unevenness of the stamper is accurately transferred to the thin film.

  Further, in the present embodiment, the thin film 33 on the sheet 31 is a single metal film, but a multilayer film including a metal reflective layer and a recording layer may be used.

  In addition, under the same conditions as described above, only the wall surface angle of the unevenness of the stamper 18 was changed, and the transfer characteristics were examined. As a result, when the wall surface angle of the unevenness of the stamper 18 was 70 degrees or less, the angle and the wall surface angle of the unevenness transferred to the thin film 33 showed a good agreement, that is, transferred accurately.

  As described above, the uneven shape formed in the thin film 33 reproduces the shape of the stamper 18 well. Therefore, unnecessary irregular reflection does not occur with respect to the laser light incident from the cover layer side, and the signal is read accurately. In general, as the thin film 33 becomes thicker, the shape of the unevenness formed on the base becomes dull. On the other hand, according to the present invention, since the unevenness is transferred after the thin film 33 is formed, there is no influence such as a dull edge of the unevenness due to the thickness of the thin film 33. Therefore, the optimum uneven shape can be determined by the uneven shape of the stamper 18, and signal optimization is easy.

  In this embodiment, a sheet 31 having a thin film 33 and a resin layer 32 that are in close contact with the stamper 18 is used, and the thin film 33 is formed as a reflective layer. However, the present invention is not limited to this, and a metal foil 30 made of a single metal element can also be used.

  In the present embodiment, aluminum is used as the thin film 33. However, the present invention is not limited to this, and the metal foil 30 and the thin film 33 may be any material having high ductility. The conditions required for the metal foil 30 and the thin film 33 are the same as the conditions required for the thin film 3 shown in the first embodiment.

[Fourth Embodiment]
In the above embodiment, the case where only one thin film 3 is provided has been described, but in reality, two or more thin films 3 are also provided in order to increase the recording capacity. Therefore, in this embodiment, an example in which two thin films 3 are provided will be described.

  FIG. 7 is a schematic process diagram for explaining a method of manufacturing an optical disc according to the fourth embodiment of the present invention. 7A, the (first) thermoplastic resin layer 2 and the (first) thin film 3 are sequentially laminated on the substrate 1. In the step shown in FIG. The steps so far are the same as those in FIG. 1B in the first embodiment described above. Subsequently, a second thermoplastic resin layer 40 is provided on the (first) thin film 3. Here, the thermoplastic resin layer 40 is formed by bonding a transparent sheet made of polycarbonate resin. Subsequently, a second thin film 41 made of silver is formed on the second thermoplastic resin layer 40 to a thickness of 50 nm by a sputtering method. Above the second thin film 41, a stamper 4 having projections and depressions (projecting pits having a track pitch of 0.35 μm and a height of 70 nm) corresponding to an information signal is disposed (FIG. 7A).

  In this state, the stamper 4 heated to 120 ° C. is brought into pressure contact with the second thin film 41 at a surface pressure of 50 MPa. At this time, it is desirable to suck the gap between the second thin film 41 and the stamper 4 so that bubbles do not enter between them. Thereby, entrainment of gas can be prevented and pressure welding can be performed effectively. As a result, the unevenness of the stamper 4 is accurately transferred to the second thin film 41 as shown in the process of FIG. 7B. Subsequently, as shown in the step of FIG. 7C, the same cover layer 5 as that of the first embodiment is formed on the second thin film 41, thereby having two thin films (reflection layers). The optical disc is completed.

  In this embodiment, the second thin film 41 (reflective layer) is provided on the substrate manufactured by the method of the first embodiment. However, on the substrate manufactured by the method of the second or third embodiment. In addition, the second thermoplastic resin layer 40 and the second thin film 41 may be provided.

  The second thin film 41 is formed by sputtering, but other vacuum film forming methods may be used. The second thin film 41 is only a metal reflective layer in the case of a reproduction type (DVD-ROM), but includes a recording layer and a metal reflection layer in the case of a write-once type or a rewritable type (DVD-RAM). It is a multilayer film of composition. By repeating the steps of the present embodiment described above, three or more transfer layers can be provided.

  As described above, the uneven shape formed in the thin film 3 and the second thin film 41 reproduces the shape of the stamper 4 well. Therefore, unnecessary irregular reflection does not occur with respect to the laser light incident from the cover layer 5 side, and the signal is read accurately. In general, when the thin film is thick, the shape of the unevenness formed on the base becomes dull. On the other hand, according to the present invention, since the unevenness is transferred after the thin film 3 and the second thin film 41 are formed, there is no influence such as a dull edge portion due to the thickness of the thin film. Therefore, the optimum uneven shape can be determined by the uneven shape of the stamper 4, and signal optimization is easy.

  In the present embodiment, silver is used for the thin film 3 and the second thin film 41. However, the present invention is not limited to this, and the thin film 3 and the second thin film 41 may be any material having high ductility. The conditions required for the thin film 3 and the second thin film 41 are the same as the conditions required for the thin film 3 shown in the first embodiment.

  As described above, according to the present invention, it is possible to obtain an optical disc in which the light transmitting cover layer has a thickness of about 0.1 mm and the unevenness formed in the reflective layer faithfully reproduces the information signal. Therefore, accurate signal reading is possible by using this optical disc. Further, since the optimum uneven shape can be determined by the uneven shape of the stamper, signal optimization is easy. As described above, the optical disc manufactured by using the manufacturing method according to the present invention is very suitable for future higher recording density.

  The optical disk of the present invention and the manufacturing method thereof are industrially available because the signal is not affected by the thickness of the metal thin film and the like, and it is possible to provide an optical disk with excellent productivity without causing wrinkles or delamination. Useful.

FIG. 5 is a schematic process diagram for explaining a method of manufacturing an optical disc according to the first embodiment of the present invention. It is a schematic sectional drawing for demonstrating the wall surface angle of the unevenness | corrugation of the stamper by the 1st Embodiment of this invention. It is a schematic sectional drawing for demonstrating the curvature radius of the edge of the upper surface and lower surface of a thin film by the 1st Embodiment of this invention. FIG. 6 is a schematic process diagram for explaining a method of manufacturing an optical disc according to a second embodiment of the present invention. It is a schematic sectional drawing of the metal mold | die used for the manufacturing method of the optical disk by the 3rd Embodiment of this invention. It is the top view and side view of a resin sheet which are used for the manufacturing method of the optical disk by the 3rd Embodiment of this invention. It is a general | schematic flowchart for demonstrating the manufacturing method of the optical disk by the 4th Embodiment of this invention. It is a schematic process diagram for explaining a conventional method for manufacturing an optical disc.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2 Thermoplastic resin layer 3 Thin film 4 Stamper 5 Cover layer 6 Transparent sheet 7 Adhesive layer

Claims (10)

A method of manufacturing an optical disc having at least a cover layer, a metal reflection layer, and a substrate in order from the direction in which laser light is incident,
The stamper supported in the cavity of the mold is directly adhered to the sheet member supported in the cavity of the mold and including at least the metal reflection layer,
The stamper has irregularities on the metal reflective layer side,
A method of manufacturing an optical disc, wherein the unevenness is transferred to the metal reflective layer and a substrate is formed on the sheet member by injecting molten resin into a cavity of the mold.   2. The method of manufacturing an optical disk according to claim 1, wherein at least the vicinity of the center of the sheet member is vacuum-sucked to the stamper side during injection of the molten resin.   The sheet member includes a resin sheet in which at least a metal reflective layer is formed on a resin layer, and the resin layer is a continuous surface, and a hole is formed in a central portion of the resin layer after filling with a molten resin. An optical disc manufacturing method according to claim 1 or 2.   The method of manufacturing an optical disk according to claim 3, wherein the metal reflective layer is provided on the resin sheet in addition to the central portion of the resin sheet.   5. The method of manufacturing an optical disk according to claim 3, wherein the substrate is formed by injecting molten resin made of the same kind of resin as the resin layer of the resin sheet into the mold.   6. The method of manufacturing an optical disc according to claim 1, wherein the outer diameter of the sheet member is smaller than the inner diameter of the cavity of the mold.   The optical disc manufacturing method according to claim 1, wherein the stamper is disposed on a surface facing a surface having a hole through which the molten resin of the mold is injected.   The optical disk manufacturing method according to claim 1, wherein a metal film containing 95 wt% or more of at least one of Au, Ag, Cu, Pt, and Al is formed as the metal reflective layer.   9. The method of manufacturing an optical disk according to claim 1, wherein a thin film including the metal reflection layer and other layers is formed so that the metal reflection layer is located on the side opposite to the stamper. The optical disc manufacturing method according to any one of the sheet member light transmission layer is 1 to claim provided comprising a transparent sheet or ultraviolet curable resin on 9.

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